A wireless communication system typically includes a base station in wireless communication with a plurality of user devices (which may also be referred to as mobile stations, subscriber units, access terminals, etc.). The base station transmits data to the users over a radio frequency (RF) communication channel. A multiple access scheme may be used to enable the users to share the communication channel without interference.
One example of a multiple access scheme that may be used is orthogonal frequency division multiple access (OFDMA). OFDMA is based on orthogonal frequency division multiplexing (OFDM). With OFDM, the transmission band of a communication channel is divided into a number of equally spaced sub-bands. A sub-carrier carrying a portion of the user information is transmitted in each sub-band, and every sub-carrier is orthogonal with every other sub-carrier. To facilitate multiple access in accordance with OFDMA, groups of sub-carriers may be assigned to different users.
The 3rd Generation Partnership Project (3GPP) is a collaboration of standards organizations throughout the world. The goal of 3GPP is to make a globally applicable third generation (3G) mobile phone system specification within the scope of the IMT-2000 (International Mobile Telecommunications-2000) standard as defined by the International Telecommunication Union. The technical work in 3GPP is organized in Technical Specification Groups (TSGs). One of the TSGs is the TSG Radio Access Network (RAN). TSG RAN is responsible for the definition of the functions, requirements and interfaces of the UTRA (UMTS Terrestrial Radio Access) network.
A proposal has been made to the 3GPP RAN-1 Working Group describing a physical layer structure for the UTRA downlink. (The term “downlink” refers to transmission from a base station to a user.) The proposal is titled “Physical Channels and Multiplexing in Evolved UTRA Downlink” (R1-050590) and is hereby incorporated by reference in its entirety. The proposed UTRA downlink utilizes OFDMA as its multiple access scheme.
One of the unique features of the proposed UTRA downlink is that it is capable of utilizing a varying number of sub-carriers for channel transmission. In other words, different users may be assigned a different number of sub-carriers. In addition, the number of sub-carriers that are assigned to a particular user may change over time. Thus, in accordance with the proposed UTRA downlink, data may be sent to different users at different transmission rates, and the data transmission rate for a particular user may change over time. This is in contrast to previous work in this area, which considered the number of sub-carriers (and hence the data transmission rate) to be fixed for all users.
Communication channels, being dispersive, are prone to block or burst errors if data is not spread uniformly over the transmission band. This is why in OFDM systems interleavers are commonly used to spread data over a multiplicity of sub-carriers, after forward error correction coding. However, to this point an interleaving/deinterleaving structure has not been defined for the proposed UTRA downlink. Accordingly, benefits may be realized by systems and methods for interleaving and deinterleaving coded data in an OFDMA-based system like the system in the proposed UTRA downlink, which is capable of utilizing a varying number of sub-carriers in order to facilitate the use of different transmission rates.